Cryostat sections for coexistence studies and preembedding electron microscopic immunocytochemistry of central and peripheral nervous system tissue

Marked Changes in Lamellar Granule and Trans-Golgi Network Structure Occur during Epidermal Keratinocyte Differentiation

Epidermal lamellar granules transport various lipids, proteins, and protein inhibitors from the trans-Golgi network to the extracellular space, and play an important role in skin barrier formation. We elucidated the 3-dimensional structure of lamellar granules and the trans-Golgi network in normal human skin by focused ion beam scanning electron microscopy. Reconstructed focused ion beam scanning electron microscopy 3-dimensional images revealed that the overall lamellar granule structure changed from vesicular to reticular within the second layer of the stratum granulosum. Furthermore, the trans-Golgi network was well developed within this layer and spread through the cytoplasm with branched, tubular structures that connected to lamellar granules. Our study reveals the unique overall 3-dimensional structure of lamellar granules and the trans-Golgi network within the cells of the epidermis, and provides the basis for an understanding of the skin barrier formation.

Role of MOG-stimulated Th1 type "light up" (GFP+) CD4+ T cells for the development of experimental autoimmune encephalomyelitis (EAE)

Experimental autoimmune encephalomyelitis (EAE) is an animal model for multiple sclerosis in humans. EAE can be passively transferred into naive syngeneic animals by administration of MOG-specific T cell clones. Lymphocytes isolated from green fluorescent protein (GFP)-transgenic (Tg) mice can light up by emitting green fluorescence, thus making it feasible to use such animals in a passive transfer model for EAE. When MOG-sensitized splenic lymphocytes from GFP-Tg mice were adoptively transferred to irradiated, syngeneic C57BL/6 and RAG-1(-/-)mice, typical symptoms of EAE developed. Analysis of the reconstituted mice with EAE revealed prominent infiltration of fluorescing (GFP+), CD4+ T cells into the central nervous system (CNS). Real-time confocal imaging revealed these cells in the spinal cords and brains of recipient mice. This infiltration was also confirmed by anti-GFP monoclonal antibodies. Furthermore, quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) evaluation indicated that the infiltrating GFP+, CD4+ T cells exclusively produced T helper type 1 (Th1) cytokines, especially interferon-gamma (IFN-gamma). These results clearly show that MOG-specific CD4+ T cells preferentially invade into the CNS and mediate the development of EAE by producing Th1-biased cytokines.

Substance P-containing hypothalamic afferents to the monkey hippocampus: an immunocytochemical, tracing, and coexistence study

In order to identify the synaptic connections of substance P-containing afferents within the hypothalamo-hippocampal projection of the monkey, we performed a combined light and electron microscopic, immunocytochemical study, made lesions of the fimbriafornix, and employed retrograde tracing using WGA-HRP. Furthermore, coexistence studies for substance P and GAD were performed to identify the putative transmitters of these hypothalamic projection neurons. A plexus of large substance P-immunoreactive terminals was identified in both the innermost portion of the molecular layer and in CA2. Axon terminals in both plexuses established exclusively asymmetric synapses with spines and dendritic shafts. Substance P-immunoreactive boutons were degenerating 5 days after lesioning, and had disappeared 10 days after ipsilateral fimbria-fornix transection. Thus, these terminals were of extrinsic origin. In contrast, immunoreactive fibers in the outer third of the dentate molecular layer remained unaffected by the lesion. Retrograde tracing combined with immunostaining for substance P revealed the parent cell bodies of the extrinsic substance P-containing afferents in the supramammillary nucleus. Colocalization studies employing a consecutive semi-thin sections technique indicate that these large substance P-containing projection neurons lack GABA as an inhibitory transmitter. These results suggest that hypothalamic afferents of the monkey hippocampus contain substance P. Because these afferents lack GABA as an inhibitory transmitter and establish exclusively asymmetric synapses, this projection may excite hippocampal target neurons.

Calretinin immunoreactivity in the monkey hippocampal formation--II. Intrinsic GABAergic and hypothalamic non-GABAergic systems: an experimental tracing and co-existence study

Our light and electron microscopic studies (Seress L., Nitsch R. and Leranth C. (1993) Neuroscience 55, 775-796.) indicated that in the hippocampus of the African Green monkey, calretinin is exclusively present in non-pyramidal cells. Calretinin-positive axons formed a prominent band at the border of the dentate molecular and granule cell layers and in the pyramidal layer of CA2, and established asymmetric synapses with different postsynaptic targets. The goal of this study is to determine the cells of origin of this presumably extrinsic innervation, and subsequently, the characterization of their neurochemical features. We were able to demonstrate that calretinin-immunoreactive axon terminals in the inner molecular layer of the dentate gyrus and in the pyramidal layer of CA2 disappear 10 days after fimbria-fornix transection. Retrograde tracing revealed their cells of origin to be in the supramammillary nucleus. Co-localization studies employing the cryostat consecutive, semithin section technique provided evidence that these large projecting neurons contained both calretinin and substance-P but lack GABA as an inhibitory transmitter. In contrast, co-localization studies revealed that almost all of the intrinsic calretinin-positive neurons in different areas of the primate hippocampus contained GAD or GABA. These results suggest that there are two separate calretinin-containing systems in the primate hippocampus, i.e. an intrinsic inhibitory and an extrinsic excitatory one, the latter deriving from the supramammillary nucleus of the hypothalamus.

Calretinin immunoreactivity in the monkey hippocampal formation--I. Light and electron microscopic characteristics and co-localization with other calcium-binding proteins

Calretinin-containing neurons were visualized by immunocytochemistry in the monkey hippocampal formation, subicular complex, and entorhinal cortex. Calretinin-immunoreactivity was present exclusively in non-granule cells of the dentate gyrus and in non-pyramidal cells of Ammon's horn, subiculum and entorhinal cortex. Most frequently, calretinin-positive neurons were found at the hilar border of the dentate granule cell layer and in the stratum radiatum of CA1-3 areas. In the subicular complex, immunoreactive neurons were evenly distributed in all layers, whereas in the entorhinal cortex, they were accumulated in external layers above the lamina dissecans. Distinct bands of calretinin-positive fibers occupied the supragranular zone of the molecular layer in dentate gyrus, the pyramidal cell layer of the CA2 area in Ammon's horn and the upper two layers of presubiculum. The majority of calretinin-immunoreactive neurons were small, bipolar or fusiform neurons with a dendritic tree oriented parallel to the dendrites of principal cells (granule cells in dentate gyrus and pyramidal neurons elsewhere). Dendrites were smooth or sparsely spiny, displaying small spines of conventional type. Co-existence studies showed that these neurons were completely devoid of other calcium-binding proteins, parvalbumin and calbindin. Electron microscopic analysis revealed somata of immunoreactive neurons which contained a large nucleus and a small cytoplasmic rim, which contained only few organelles. The nucleus displayed deep infoldings and intranuclear rods. Input synapses of immunoreactive neurons were rare both on somata and dendrites and large surface areas were frequently apposed by glial processes. This was very prominent in the dentate gyrus and Ammon's horn. Axons of calretinin-positive neurons were thin, arborized in all layers and had small varicosities. Their terminals formed symmetric synaptic contacts mainly with dendrites and less frequently with somata of principal cells. Axon terminals of calretinin-immunoreactive fiber bundles in the supragranular layer, as well as in the pyramidal layer of the CA2 area, formed asymmetric synaptic contacts with dendritic shafts. In addition, they established asymmetric axospinous and axosomatic synaptic contacts with granule cells of the dentate gyrus. In the presubiculum, the calretinin-positive axon bundle included a large number of immunoreactive myelinated axons, as well as axon terminals. The characteristic location and features of synapses suggests that these fibers derive from extra-hippocampal afferents (Nitsch, R. and Leranth C. (1993) Neuroscience 55, 797-812) and not from the calretinin-immunoreactive neurons of the hippocampal formation.

Neuropeptide Y (NPY)-immunoreactive neurons in the primate fascia dentata; occasional coexistence with calcium-binding proteins: a light and electron microscopic study

Neuropeptide Y (NPY)-containing neurons are known to be highly vulnerable following sustained electrical stimulation in rats and in humans suffering from temporal lobe epilepsy. This has been related to a strong excitatory input. In contrast, there is evidence that neurons containing calcium-binding proteins exhibit a high resistance under experimental seizure and hypoxia conditions. The aim of this study was to determine the coexistence of NPY and calcium-binding proteins in inhibitory neurons of the primate fascia dentata and their synaptic connections. Vibratome sections of hippocampi of African green monkeys (Cercopithecus aethiops) were immunostained with antibodies against NPY, PARV, and CB. A quantitative coexistence study was performed for NPY and PARV on consecutive semithin sections. In contrast to the rodent hippocampus, NPY-immunoreactive neurons were found exclusively in the hilus of fascia dentata with horizontally oriented dendrites which did not extend into the granular and molecular layer. Conversely, PARV-immunoreactive neurons were also present in the granular and inner molecular layer and extended their dendrites far out in the molecular layer and the hilus. Axon terminals immunoreactive for NPY were mostly concentrated in the middle and outer molecular layer and the hilar region and were rare in the granular layer. PARV-immunoreactive boutons were basically restricted to the granular layer where they formed typical baskets. The antibody against calbindin stained almost exclusively granule cells. Coexistence of NPY- and PARV-immunoreactivity was found only in hilar neurons and was rare (9 out of 152 cells analyzed). These results suggest that most NPY-immunoreactive neurons do not contain calcium-binding proteins. NPY-containing neurons exhibited ultrastructural characteristics as described for inhibitory neurons. Their dendrites were only sparsely contacted by mostly asymmetric synaptic terminals, including a very small number of mossy fiber axon terminals. In turn, numerous NPY-immunoreactive axon terminals formed symmetric synapses with spines and dendritic shafts of unlabeled neurons in the middle and outer molecular layer, whereas no contact with granule cell bodies was evident. Thus, we conclude that the vulnerability of NPY-containing inhibitory neurons may be due more to the lack of calcium-binding proteins than to a strong excitatory innervation. As their axons may contribute to the inhibitory control of the major excitatory input from the entorhinal cortex, their loss following overstimulation may play a role in perpetuating hippocampal seizure activity.

Area-specific morphological and neurochemical maturation of non-pyramidal neurons in the rat hippocampus as revealed by parvalbumin immunocytochemistry

The time course of the morphological differentiation of non-pyramidal neurons in the rat hippocampus shows an area specificity. Thus, non-pyramidal neurons in CA3 appear more mature than in CA1 at early postnatal stages. Physiological data provide evidence for an earlier maturation of GABA-mediated inhibition in CA3 in comparison to CA1. As the calcium-binding protein parvalbumin (PARV) is thought to be a marker for highly active inhibitory neurons, we analyzed the area-specific appearance of PARV in GABAergic neurons during development. Employing combined light and electron microscopic immunocytochemistry, we revealed an area specificity in the time course of the neurochemical and morphological maturation of this functionally important subpopulation of non-pyramidal cells. The first appearance of PARV-immunoreactivity was observed at P7 and was exclusively located in cell bodies in CA3. At P8, neurons in CA3 exhibited PARV-immunoreactivity in cell bodies and dendrites, but very rarely in axon terminals. These neurons displayed the typical light and electron microscopic characteristics of GABAergic non-pyramidal cells. At P10, axon terminals formed typical baskets surrounding the pyramidal cells. The appearance of PARV-immunoreactivity in cell bodies, dendrites and axon terminals in CA1 was noticed about 1 to 2 days later. In the fascia dentata, non-granule cells displayed immunoreactivity not before P10. These data indicate a sequential neurochemical and morphological maturation of non-pyramidal neurons that may be related to differences in the maturation of inhibition during hippocampal development.

Late appearance of parvalbumin-immunoreactivity in the development of GABAergic neurons in the rat hippocampus

The calcium-binding protein parvalbumin (PARV) is supposed to have a protective function under conditions of experimental seizure and hypoxia in a subgroup of GABAergic inhibitory neurons in the adult rat hippocampus. Here we studied the appearance of PARV immunoreactivity in rat hippocampal non-pyramidal cells during postnatal development in comparison to glutamate decarboxylase (GAD) immunoreactivity. PARV-immunoreactive neurons were not observed before postnatal day 7 whereas GAD-positive neurons and terminal-like puncta were present at postnatal day 2 (P2) and were frequent around P5. From other studies it is known that all GABAergic neurons are formed prenatally. Our data thus indicate that in the early postnatal period GABAergic non-pyramidal cells are poorly protected by calcium-binding proteins against a pathological calcium influx.

Most somatostatin-immunoreactive neurons in the rat fascia dentata do not contain the calcium-binding protein parvalbumin

A selective loss of somatostatin (SS)-containing neurons in the hilar region has been reported in patients suffering from temporal lobe epilepsy. Conversely, neurons containing calcium-binding proteins such as parvalbumin (PARV) are known to be very resistant under experimental seizure conditions. In this study, we analyzed the coexistence of SS and PARV in neurons of the rat fascia dentata by using serial semi-thin cryostat sections for pre-embedding immunocytochemistry. Our results show that only 5.7% of the SS-immunoreactive hilar neurons contain PARV. The data suggest that SS-containing hilar neurons are less protected against seizure-induced calcium overload than other neurons containing calcium-binding proteins.

The parvalbumin-containing nonpyramidal neurons in the rat hippocampus

The calcium-binding protein parvalbumin is considered to be involved in the control of intracellular ion homeostasis of highly active inhibitory neurons. A review of the light and electron microscopical features as well as the identified synaptic connections of these neurons is presented. Parvalbumin-containing neurons are mostly located within or in the vicinity of the granule or pyramidal cell layer. They form a subgroup of GABAergic neurons that has a target specificity for the cell body region. Their fine structural characteristics are identical to those known for hippocampal inhibitory neurons. Parvalbumin-containing neurons are involved in several inhibitory pathways: feed-back inhibition, feed-forward inhibition and disinhibition. The functional implications of our own as well as published data are discussed. Special consideration is given to the possible physiological role of parvalbumin in these neurons.